The specificities and numbers of lymphocytes in animals are tightly controlled to avoid autoimmunity and to avoid accumulation of lymphocytes generated during previous infections. This control can be achieved through the death of autoreactive lymphocytes as consequence of selection events. Similarly, many lymphocytes that are generated in response to infections die when the infectious agent disappears. The lymphocyte repertoire is also influenced by the ability of lymphocytes to alter their antigen receptor. For example, the antigen receptor expressed by some autoreactive lymphocytes can be modified either by deletion of the genes encoding the offending receptor, or by silencing the action of the autoreactive receptor. At the peak of an immune response against a natural infection, a host can generate pathogen-specific T cell responses that comprise 20-50% of the hosts'total T cell pool. We have now identified a vaccination strategy that is able to generate a similar level of T cell expansion from a purely molecular based vaccine, a result not possible with previously developed vaccine strategies. These high levels of CD8+ T cell expansion can be achieved by the vaccination of a host with antigen in combination with agonists for both the Toll-Like Receptor (TLR) and CD40 pathways. We now have preliminary data demonstrating that both primary and memory CD8+ T cell responses elicited by combined TLR/CD40-agonist immunization occur independent of the presence of CD4+ T cells. This is in contrast to other immunization techniques in which memory CD8+ T cell responses are critically dependent upon the presence of CD4+ T cells. In the studies proposed here, the mechanism by which this immunization can generate CD4 independent CD8+ T cell responses will be investigated. These studies will yield information vital to the understanding of how potent cellular immunity can be generated even in the context of CD4 deficiency. Understanding these mechanisms is of critical importance, particularly for disease conditions where the existence of CD4+ T cell response is uncertain, such as in cancer, or is known to be absent and/or deficient, such as in HIV. These studies will lead to the development of more potent vaccines against these kinds of diseases whose treatment seems to require the quantity and quality of cellular immunity that only combined TLR/CD40-agonist immunization is capable of generating.